What are all odd numbers must end in one of five digits?

All odd numbers must end in one of the following five digits: 1, 3, 5, 7, or 9. This is because odd numbers are defined as integers that cannot be evenly divided by 2, and these digits ensure that the number does not end in an even digit (0, 2, 4, 6, or 8). Therefore, any odd number will always conclude with one of these five specific digits.